Mechanical forces are important modulators of cellular function in many tissues. For example, mechanotransduction responses to laminar or disturbed flow can strongly affect the ability of endothelial cells to maintain the barrier between blood and the vessel wall. Laminar flow occurs in straight vessels and produces a steady shear stress on the cells. Disturbed flow forms downstream of obstructions, bends, or bifurcations, and produces a time-averaged, low shear stress due to eddies in the flow. These flows can activate mechanosensors in endothelial cells that lead to the activation of signaling pathways that affect cytoskeletal structures. In particular, laminar flow can initiate Rho GTPase pathways that cause alignment of actin filaments and assembly of adherens junctions. Conversely, disturbed flow leads to disorganized actin, disassembly of adherens junctions, and small gaps between adjacent endothelial cells. These structural changes in endothelial cells can strongly affect the integrity of the vascular barrier.